The invention relates to a method of checking the performance of catalysts in internal-combustion engines, which catalysts have the task of reducing pollutants existing in the engine exhaust gas.
A method of checking the efficiency of a catalyst is known from German Patent Document DE 37 19 174 A1. In the case of this known method, the mixture ratio of the gas constituents of the gas mixture flowing into the catalyst is compared with the mixture ratio of the gas constituents of the gas mixture flowing out of the catalyst. By means of this result, an evaluation of the catalyst performance is carried out. The catalyst performance, for example, is determined with respect to the correlation between the HC conversion capacity and the oxygen storage capacity of the catalyst. The oxygen storage capacity is measured oxygen probes, which are arranged in front of and behind the catalyst.
On the basis of the ratio of the pollutant concentration in front of and behind the catalyst, a so-called conversion rate is determined. At a conversion rate of approximately 100%, the catalyst is recognized to be in full working order; whereas, for example, at a conversion rate of less than 92%, the catalyst is found to no longer be in working order.
The monitoring of the performance of the catalyst is necessary because defects at the catalyst can considerably increase the exhaust gas emissions. For this reason, it is endeavored to improve the monitoring of the catalyst and therefore meet the strict exhaust emission standards and the increasing demands for on-board diagnosis (OBD).
In comparison with the known evaluation method, the method of checking the catalyst performance in an internal-combustion engine has the advantage that a relatively large number of exhaust gas parameters (such as concentration), which are measured in similar selected operating conditions of the internal-combustion engine, according to statistical methods, are condensed to an up-to-date average exhaust gas value. This value is backed statistically, can be assessed with respect to its informational precision, and correlates with the quality of the catalyst performance. The up-to-date average exhaust gas value is compared with an exhaust gas threshold value which, in turn, was determined via a threshold value catalyst which was aged in a defined manner. In the case of the suggested method according to the invention, a second sensor in front of the catalyst can be eliminated. Because the differences between the exhaust gas conversion from a new catalyst to an aged or defective catalyst are the clearest in transient conditions, such as acceleration and deceleration when the engine and the catalyst system are running hot, by means of the method according to the invention, an evaluation of the catalyst performance can intentionally take place under these operating conditions. It is therefore not necessary to pass through all kinds of driving conditions in order to evaluate the catalyst performance and permanently monitor these operating conditions, particularly the less critical ones, whereby the control unit is in turn relieved of unnecessary computing operations.
Advantageous further developments and improvements of the method according to the invention can be achieved.
The determination of the exhaust gas value to be compared in an up-to-date manner from a number of similar past values has the advantage that the measurements are statistically backed and the evaluation therefore takes place on the basis of a sufficiently large number of measured values. A very simple and informative variant for summarizing a definable number of measured values is the formation of an average value. Likewise, it is possible, although it is not explained in detail in the following, to form the center of gravity of a surface or the integral by way of the definable number of measured exhaust gas values.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.
FIG. 1 is a basic block diagram of an engine with a catalyst that is monitored;
FIG. 2 is a flow chart of the method according to the present invention in a general form; and
FIG. 3 is a flow chart of the method according to the present invention in a detailed form.